123 research outputs found
Tilted axis rotation, candidates for chiral bands, and wobbling motion in 138Nd
High-spin states in 138Nd were investigated using the reaction 94Zr(48Ca,4n), detecting coincident γ rays with the gasp spectrometer. A rich level scheme was constructed including four bands of negative parity at low spins, eight bands of dipole transitions, and eight bands of quadrupole transitions at medium spins. The cranked shell model and the tilted-axis cranking model are used to assign configurations to the observed bands, where zero pairing is assumed. For selected configurations the case of finite pairing is also considered. A consistent notation for configuration assignment that applies for both zero and finite pairing is introduced. The observed bands are interpreted as rotation around the short and long principal axes (quadrupole bands), as well as around a tilted axis (dipole bands). The dipole bands have an intermediate character, between magnetic and collective electric rotation. A pair of dipole bands is identified as candidates for chiral partners. The possible existence of the wobbling mode at low deformation and medium spins is discussed. The consistent interpretation of the multitude of observed bands strongly supports the existence of stable triaxial deformation at medium spins in 138Nd. ©2012 American Physical Societ
Anisotropic colloids through non-trivial buckling
We present a study on buckling of colloidal particles, including
experimental, theoretical and numerical developments. Oil-filled thin shells
prepared by emulsion templating show buckling in mixtures of water and ethanol,
due to dissolution of the core in the external medium. This leads to
conformations with a single depression, either axisymmetric or polygonal
depending on the geometrical features of the shells. These conformations could
be theoretically and/or numerically reproduced in a model of homogeneous
spherical thin shells with bending and stretching elasticity, submitted to an
isotropic external pressure.Comment: submitted to EPJ
Algebraic structure of gravity in Ashtekar variables
The BRST transformations for gravity in Ashtekar variables are obtained by
using the Maurer-Cartan horizontality conditions. The BRST cohomology in
Ashtekar variables is calculated with the help of an operator
introduced by S.P. Sorella, which allows to decompose the exterior derivative
as a BRST commutator. This BRST cohomology leads to the differential invariants
for four-dimensional manifolds.Comment: 19 pages, report REF. TUW 94-1
3D Brownian Diffusion of Submicron-Sized Particle Clusters
We report on the translation and rotation of particle clusters made through
the combination of spherical building blocks. These clusters present ideal
model systems to study the motion of objects with complex shape. Because they
could be separated into fractions of well-defined configurations on a
sufficient scale and their overall dimensions were below 300 nm, the
translational and rotational diffusion coefficients of particle duplets,
triplets and tetrahedrons could be determined by a combination of polarized
dynamic light scattering (DLS) and depolarized dynamic light scattering (DDLS).
The use of colloidal clusters for DDLS experiments overcomes the limitation of
earlier experiments on the diffusion of complex objects near surfaces because
the true 3D diffusion can be studied. When the exact geometry of the complex
assemblies is known, different hydrodynamic models for calculating the
diffusion coefficient for objects with complex shapes could be applied. Because
hydrodynamic friction must be restricted to the cluster surface the so-called
shell model, in which the surface is represented as a shell of small friction
elements, was most suitable to describe the dynamics. A quantitative comparison
of the predictions from theoretical modeling with the results obtained by DDLS
showed an excellent agreement between experiment and theory
Absence of VHL gene alteration and high VEGF expression are associated with tumour aggressiveness and poor survival of renal-cell carcinoma
International audienceBACKGROUND: The von Hippel-Lindau gene (VHL) alteration, a common event in sporadic clear-cell renal-cell carcinoma (CCRCC), leads to highly vascularised tumours. Vascular endothelial growth factor (VEGF) is the major factor involved in angiogenesis, but the prognostic significance of both VHL inactivation and VEGF expression remain controversial. The aims of this study were to analyse the relationship between VHL genetic and epigenetic alterations, VHL expression and VEGF tumour or plasma expression, and to analyse their respective prognostic value in patients with CCRCC. METHODS: A total of 102 patients with CCRCC were prospectively analysed. Alterations in VHL were determined by sequencing, Multiplex Ligation-dependent Probe Amplification (MLPA) and methylation-specific MLPA. Expression of pVHL and VEGF was determined by immunohistochemistry. Plasma VEGF was measured by enzyme-linked immunosorbent assay (ELISA). RESULTS: VHL mutation, deletion and promoter methylation were identified in 70, 76 and 14 cases, respectively. Overall, at least one VHL-gene alteration occurred in 91 cases (89.2%). Both VEGF tumour and plasma expression appeared to be decreased in case of VHL alteration. Median progression-free survival and CCRCC-specific survival were significantly reduced in patients with wild-type VHL or altered VHL and high VEGF expression, which, therefore, represent two markers of tumour aggressiveness in CCRCC. CONCLUSION: Stratifying CCRCCs according to VHL and VEGF status may help tailor therapeutic strategy
Patterning symmetry in the rational design of colloidal crystals
Colloidal particles have the right size to form ordered structures with periodicities comparable to the wavelength of visible light. The tantalizing colours of precious opals and the colour of some species of birds are examples of polycrystalline colloidal structures found in nature. Driven by the demands of several emergent technologies, efforts have been made to develop efficient, self-assembly-based methodologies for generating colloidal single crystals with well-defined morphologies. Somewhat unfortunately, these efforts are often frustrated by the formation of structures lacking long-range order. Here we show that the rational design of patch shape and symmetry can drive patchy colloids to crystallize in a single, selected morphology by structurally eliminating undesired polymorphs. We provide a proof of this concept through the numerical investigation of triblock Janus colloids. One particular choice of patch symmetry yields, via spontaneous crystallization, a pure tetrastack lattice, a structure with attractive photonic properties, whereas another one results in a colloidal clathrate-like structure, in both cases without any interfering polymorphs
Low-lying octupole isovector excitation in Nd-144
International audienceThe nature of low-lying 3â levels in Nd144 was investigated in the Nd143(n,γγ) cold neutron-capture reaction. The combination of the high neutron flux from the research reactor at the Institut Laue-Langevin and the high Îł-ray detection efficiency of the EXILL setup allowed the recording of γγ coincidences. From the coincidence data precise branching ratios were extracted. Furthermore, the octagonal symmetry of the setup allowed angular-distribution measurements to determine multipole-mixing ratios. Additionally, in a second measurement the ultra-high resolution spectrometer GAMS6 was employed to conduct lifetime measurements using the gamma-ray induced Doppler-shift technique (GRID). The confirmed strong M1 component in the 33ââ31â decay strongly supports the assignment of the 33â level at 2779keV as low-lying isovector octupole excitation. Microscopic calculations within the quasiparticle phonon model confirm an isovector component in the wave function of the 33â level, firmly establishing this fundamental mode of nuclear excitation in near-spherical nuclei
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